1. Field of the Invention
The present invention relates to a method for controlling an internal combustion engine including an exhaust gas recirculation (EGR) system.
2. Background Art
In the control of internal combustion engines, the conventional practice utilizes an engine controller with inputs, outputs, and a processor that executes instructions to control the engine including its various systems. The engine may include a variable geometry turbocharger (VGT) system and an exhaust gas recirculation (EGR) system. U.S. Pat. No. 6,305,167 describes an existing method of controlling an engine. The engine business is quite competitive. Increasing demands are being placed on manufacturers to provide improved performance, reliability, and durability while meeting increasing emissions requirements.
An EGR system introduces a metered portion of exhaust gases through an EGR valve into the intake manifold of the engine. The exhaust gases lower combustion temperatures to reduce the level of oxides of nitrogen (NOx) that are produced. The EGR valve itself may take any suitable form such as a butterfly valve. The EGR system has been used on many engines, including heavy-duty diesel engines. Sometimes, these heavy duty diesel engines employ a turbocharger system such as a variable geometry turbocharger (VGT) system in addition to the EGR system.
Exhaust gas recirculation (EGR) is considered one of the enabling technologies for reduction of NOx emission in diesel engine exhaust. And the reduction of NOx using EGR usually comes with an increase in particulate matters (PM) emission. To achieve the best trade-off of NOx, vs. PM, precise engine control, including the control of EGR flow rate especially, is critical. The control strategy for diesel engines equipped with EGR requires time-averaged EGR flow rate as an input parameter and the current technology is to use an orifice or venturi type of flow meter in the EGR circuit to directly measure EGR flow rate. Because the EGR flow, usually taken from turbo housing or exhaust manifold, is highly pulsating, it is a technical challenge to obtain accurate EGR flow rate measurement and its time averaged value. In addition, the flow meter increases the flow restrictions in the EGR circuit and could also be contaminated by the soot-containing EGR flow, resulting in loss of accuracy or even sensor malfunction.
For the foregoing reasons, there is a need for an improved method for controlling an engine.
It is, therefore, an object of the present invention to provide an improved method for controlling an engine with an EGR system in which EGR flow rate is determined without direct measurement of it in the EGR circuit.
In carrying out the above object, a method for controlling an internal combustion engine is provided. The engine includes an engine block defining a plurality of cylinders, an intake manifold for supplying air to the plurality of cylinders, a controller, and an exhaust gas recirculation (EGR) system. The EGR system introduces a metered portion of exhaust gases to the intake manifold. The controller communicates with the EGR system to control the engine. The method comprises determining an air mass flow rate through the intake manifold at a location upstream of the exhaust gas introduction. The method further comprises determining an engine speed, determining an intake manifold air density, and determining an engine volumetric efficiency. The engine volumetric efficiency is based on the engine speed and the intake manifold air density. The method farther comprises determining an EGR flow rate based on the volumetric efficiency, the intake manifold air density, an engine displacement volume, the engine speed, and the intake manifold air mass flow rate. The method further comprises controlling the engine based on the EGR flow rate.
Further, in carrying out the present invention, an internal combustion engine is provided. The engine includes an engine block defining a plurality of cylinders, an intake manifold for supplying air to the plurality of cylinders, a controller, and an exhaust gas recirculation (EGR) system. The EGR system introduces a metered portion of exhaust gases to the intake manifold. The controller communicates with the EGR system to control the engine. The controller is programmed to control the internal combustion engine by determining an air mass flow rate through the intake manifold at a location upstream of the exhaust gas introduction. An engine speed and an intake manifold air density are determined. An engine volumetric efficiency is determined based on the engine speed and the intake manifold air density. An EGR flow rate is determined. The EGR flow rate is based on the volumetric efficiency, the intake manifold air density, an engine displacement volume, the engine speed, and the intake manifold air mass flow rate. The engine is controlled based on the EGR flow rate.
It is to be appreciated that methods and engines of the present invention may utilize a wide variety of techniques to determine the intake manifold air mass flow rate, and the engine may include a variable geometry turbocharger (VGT) system. Suitable air mass flow rate determination techniques include hot-wire or hot-film based techniques at the compressor inlet to measure fresh charge air flow, as well as equivalent techniques that, for example, make determinations based on pressure and temperature during the stable flow process at the compressor.
In one embodiment, determining the engine volumetric efficiency further comprises determining an engine exhaust to intake pressure ratio. A correction factor based on the engine exhaust to intake pressure ratio is determined. The engine volumetric efficiency is further based on the correction factor.
In another embodiment, determining the engine volumetric efficiency further comprises establishing a neural network. The neural network receives the engine speed, an intake manifold air pressure, an intake manifold air temperature, and an exhaust pressure as inputs, and provides the engine volumetric efficiency as an output.
Preferably, determining the EGR flow rate further comprises determining the EGR flow rate according to
{dot over (m)}EGR=xcex7vxcfx81a,iVdN/2xe2x88x92{dot over (m)}charge 
where xcex7v is the engine volumetric efficiency, xcfx81a,i is the intake manifold air density, Vd is the engine displacement volume, N is the engine speed, {dot over (m)}charge is the intake manifold air mass flow rate, and {dot over (m)}EGR is the EGR flow rate. This equation is applicable for a 4 cycle internal combustion engine and would be modified if applied to a 2 cycle internal combustion engine.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the preferred embodiment when taken in connection with the accompanying drawings.